Inspired by these two questions:
Why was the image of Supreme Leader Snoke not "scaled to fit our primitive screens"?
Did Kylo Ren ever actually start training with Snoke?
Do we know if Kylo has met Snoke in person? One would think if the relationship is akin to the Vader/Palpatine one, then they most certainly have. Is there any concrete evidence?
Yes, as seen in The Last Jedi.
We see Ren (and Hux) in Snoke's chambers early on in the movie.
Later on,
Ren returns to Snokes chambers with Rey. Snoke tasks Ren with killing Rey, but Ren kills Snoke instead, and the two temporarily join forces to take on Snokes elite praetorian guards.
In the Legends book Darth Plagueis, Plagueis states that the most important information and the best training comes from one on one lessons between master and apprentice. Not through other means like holocrons and transmissions. Also in the movie Snoke recalls Kylo and says, "We must complete your training," suggesting that they have started and then halted to execute some plans.
The only problem with any of this is that I don't think Snoke is a Sith Lord so he may not adhere to the same rules. As for hard concrete evidence, we will have to see. Abrams hasn't said much.
Sidious remained silent for a long moment. “Am I to be equally distrustful of the lessons contained in Sith Holocrons?” “Not distrustful,” Plagueis said gravely. “But holocrons contain knowledge specific and idiosyncratic to each Sith who constructed them. Real knowledge is passed by Master to apprentice in sessions such as this, where nothing is codified or recorded—diluted—and thus it cannot be forgotten. There will come a time when you may wish to consult the holocrons of past Masters, but until then you would do better not to be influenced by them. You must discover the dark side in your own way, and perfect your power in your own fashion. All I can do in the meantime is help to keep you from losing your way while we hide in plain sight from the prying eyes of our enemies.”
